1. Field of the Invention
The present invention relates to an optical disk device, and more particularly to a high-definition optical disk device which uses grooves and lands for data recording and reproducing.
2. Description of Related Art
HD (High-Definition) DVDs have been proposed in recent years as next generation DVDs. It is intended that the HD-DVDs adopt the disk structure of the current DVDs so as to ensure compatibility therewith, while simultaneously achieving higher density data recording than that of previous generation DVDs.
As one main feature, HD-DVDs adopt the land/groove recording method in which information is recorded in both lands and grooves. Land tracks and groove tracks are formed in wobbles, in which address information is embedded. More specifically, address information is expressed using phase modulation in such a manner that a phase of 0 degree indicates “0” and a phase of 180 degrees indicates “1”. Here, for the address information to be embedded in the form of wobbles, binary data are converted into a gray code in which the distance between codes (inter-code distance) for adjacent sets of binary data, that is, the number of inverted bits, is equal to 1. Accordingly, in gray code, address “0” is represented as “00000000”; address “1” is represented as “00000001”; address “2” is repented as “00000011”; address “3” is represented as “00000010”; address “4” is represented as “00000110”, and so on.
Wobbles of an HD-DVD are shown schematically in FIG. 9. In one groove track, with a combination “0” represented by wobbles in a phase of 0 degree both at the inner radius and the outer radius of the disk and “1” represented by wobbles in a phase of 180 degrees both at the inner radius and the outer radius of the disk, address information of “0001” is embedded. In the next groove track address information of “0011” is embedded in a similar manner, with a combination of “0” and “1” represented by wobbles having phases of 0 and 180 degrees, respectively. In the land track disposed between these two groove tracks, however, wobbles at the inner radius and wobbles at the outer radius become out of phase with respect to each other at the inversed bit position of the contiguous groove track (the bit position 100 in FIG. 9), where a wobble signal cannot be specified.
In order to address the above problem, HD-DVDs include respective regions where either the land track address or the groove track address are to be exclusively embedded. These regions are provided such that they are displaced from each other in the track direction, whereby the land track address and the groove track address are formed. When reading address information of a land track, the exclusive region for groove is skipped and the track address in the exclusive region for land that follows the exclusive groove region is read.
FIG. 10 schematically shows the address structure of an HD-DVD. Referring to FIG. 10, the exclusive regions for grooves and lands are indicated as “G track address systems” and “L track address systems”, respectively. Each of the groove tracks and land tracks is divided into a plurality of segments in the track direction. The segment addresses are sequentially assigned for each track along circumference of the disk and are then reset for the following track. Consequently, segment 1 of groove N is adjacent to segment 1 of land N, which is then adjacent to segment 1 of groove N+1.
In the G track address system of groove N, address “N” is embedded only with wobbles which are in phase with each other (in-phase wobbles), and in the L track address system of the adjacent land N, address “N” is embedded only with in-phase wobbles. Thus, when tracing the groove track N (groove N), the segment and a wobble signal in the G track address system are reproduced. When tracing the land track N (land N), after reading the segment, the G track address system is skipped and a wobble signal in the L track address system is reproduced, thereby obtaining address information. The address structure of HD-DVDs is disclosed in “Nikkei Electronics, Oct. 13, 2003”, Nikkei BP, Oct. 13, 2003, pp. 126-134.
As described above, because, for tracing land N, the G track address system is skipped and the L track address system is read, the G track address system indicated by A in FIG. 10 becomes unnecessary or a useless region. Similarly, when tracing groove N+1, because the L track address system is not used, the L track address system indicated by B in FIG. 10 becomes a useless region. While these regions include wobbles in opposite phase and provide only undetermined address information, it is desirable to effectively utilize such information.